The regulation of extracellular signal-regulated protein kinase (ERK) 1/2 and p38 phosphorylation on 0.1 mM sodium nitroprusside (SNP) pretreated chondrocytes. (a) Chondrocytes were treated with 0.1 mM SNP 14 hours prior to treatment with 1 mM SNP and the phosphorylations of ERK 1/2 and p38 were analyzed after 4 hours by western blotting. Protein was extracted from chondrocytes and 20 μg each protein sample was separated by 12% SDS-PAGE and blotted with anti-phospho-ERK 1/2 or anti-phospho-p38. The expressions of ERK 1/2 and p38 were also determined by western blot analysis. Data are representative of samples from four different donors. (b) Effect of ERK 1/2 and p38 kinase inhibition on the chondrocyte death induced by 1 mM SNP. Cell death was induced by treating chondrocytes with 1 mM SNP for 24 hours. To inhibit ERK 1/2 or p38 kinase, chondrocytes were pretreated with 10, 20, or 50 μM PD98059 or with 1, 5, or 10 μM SB202190, respectively, for 2 hours before treating them with 1 mM SNP. Cell death was quantitated by the 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazdium bromide assay. Cell survival in control culture was set at 100%. Data are the means and standard deviations of duplicate experiments from at least three different donors. * P < 0.05 versus treatment with 1 mM SNP without pretreatment.